Watford - Watford forward Mauro Zarate was taken to hospital for scans on a serious knee injury suffered during his side's 1-1 draw with 10-man West Ham on Saturday.
Zarate had won the penalty that Troy Deeney converted to give Watford an early lead at Vicarage Road, but the former West Ham star's evening turned sour just before half-time.
After crumpling in a heap when he twisted awkwardly during a West Ham attack, Zarate needed lengthy treatment before being stretchered off with an oxygen mask over his face and his right leg in a heavy strapping as all four sides of the stadium rose to applaud him.
The 29-year-old Argentine was sent to hospital to check the severity of the problem and Watford were unable to hold onto the lead without him.
Ghana striker Andre Ayew came off the bench to equalise in the second half and West Ham held on despite Michail Antonio's late dismissal for a second booking for handball.
Zarate had made an immediate impact against his former side, darting into the area to meet Deeney's pass before being sent sprawling to the turf by Cheikhou Kouyate in the third minute.
Deeney rolled in the penalty for his fourth goal in his last five Premier League appearances.
West Ham pushed for an equaliser and Younes Kaboul did superbly to block a goal-bound Robert Snodgrass shot before sticking out a foot to prevent Antonio from equalising.
Zarate's injury cast a shadow over the match and West Ham took advantage of the dip in Watford's display.
Hammers boss Slaven Bilic was furious when Kouyate was wrestled to the ground by M'Baye Niang in the area, only for referee Craig Pawson to wave play on.
But West Ham equalised in the 73rd minute after Antonio outpaced Kaboul before seeing his shot clip the near post, roll along the goal-line and back out off the far post for Ayew to sidefoot in his second goal for the club.
Antonio, who had been booked in the first half, saw red for deliberately handling after he had been tackled, but the 10 men managed to survive a late Watford onslaught.